1. Field of the Invention
The invention relates to a variable valve timing apparatus for an internal combustion engine, which includes a variable valve timing mechanism that changes the valve timing, a phase locking mechanism that locks the valve timing at an intermediate timing between the most advanced timing and the most retarded timing, and a hydraulic pressure control mechanism that hydraulically actuates these variable valve timing mechanism and the phase locking mechanism.
2. Description of the Related Art
The variable valve timing apparatus is, for example, known as the one described in Japanese Patent Application Publication No. 2001-50064 (JP-A-2001-50064). As is described in the paragraphs [0035] to [0043] and FIG. 3 to FIG. 6 of JP-A-2001-50064, the variable valve timing apparatus includes a variable valve timing mechanism, a phase locking mechanism and a hydraulic pressure control mechanism. The variable valve timing mechanism changes the valve timing of an intake valve between the most advanced timing and the most retarded timing. The phase locking mechanism locks the valve timing of the intake valve at an intermediate timing between the most advanced timing and the most retarded timing. The hydraulic pressure control mechanism hydraulically actuates these variable valve timing mechanism and phase locking mechanism.
In addition, the phase locking mechanism is formed of an intermediate chamber, a restricting member and a restricting hole. The intermediate chamber is in fluid communication with retard chambers of the variable valve timing mechanism. The restricting member is provided for an output rotor and is displaced with respect to the output rotor between a lock position and a release position. The restricting hole is formed in an input rotor. The restricting member can be fitted into the restricting hole. In addition, the hydraulic pressure control mechanism includes a single control valve that supplies or drains lubricating oil (working oil) to or from each of the variable valve timing mechanism and the phase locking mechanism.
Then, when the relative rotational phase between the input rotor and output rotor of the variable valve timing mechanism corresponds to the intermediate valve timing, and when lubricating oil is supplied to the intermediate chamber via one of the retard chambers by the control valve, the restricting member projects from the output rotor and is displaced to the lock position. Thus, a relative rotation between the input rotor and the output rotor is restricted to lock the valve timing at the intermediate timing. On the other hand, when the relative rotational phase between the input rotor and output rotor of the variable valve timing mechanism corresponds to the intermediate valve timing, and when lubricating oil is drained from the intermediate chamber via the one of the retard chambers by the control valve, the restricting member withdraws from the restricting hole and is displaced to the release position. Thus, the restriction of a relative rotation between the input rotor and the output rotor is removed to allow the valve timing to be changed.
Incidentally, in the variable valve timing apparatus, the valve timing is locked by the phase locking mechanism only when the engine is stopped; however, in order to further, effectively take advantage of the function of the phase locking mechanism, it may be desirable that the valve timing can be locked during operation of the engine as well. However, the variable valve timing apparatus is formed so that one of the retard chambers is in fluid communication with the intermediate chamber. Therefore, in order to lock the valve timing during operation of the engine, it is necessary to drain lubricating oil from the retard chambers, that is, to set the operation mode of the control valve to an advance mode. On the other hand, the advance mode premises to respond to an advance request based on an engine operating state in normal valve timing control, so the rate of change in the valve timing is high when the advance mode is selected. Therefore, when the advance mode is selected as the mode of the control valve in order for the phase locking mechanism to lock the valve timing, the restricting member may not be fitted into the restricting hole but may pass by the restricting hole. Thus, the valve timing may not be appropriately locked by the phase locking mechanism.
Then, to solve the above problem, it is conceivable that both a control valve for the variable valve timing mechanism and a control valve for the phase locking mechanism are provided and then these control valves are separately controlled. However, in this case, two control valves are required, so it may not be desirable in terms of practical use.